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Steal the light: shade vs fire adapted vegetation in forest–savanna mosaics
Author(s) -
CharlesDominique Tristan,
Midgley Guy F.,
Tomlinson Kyle W.,
Bond William J.
Publication year - 2018
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.15117
Subject(s) - interception , canopy , biome , shading , dominance (genetics) , biomass (ecology) , shade tolerance , leaf area index , environmental science , specific leaf area , pruning , tree canopy , chronosequence , agroforestry , agronomy , biology , ecology , botany , ecosystem , photosynthesis , art , biochemistry , gene , visual arts
Summary Shade cast by trees, which suppresses grass growth, and fire fuelled by grass biomass, which prevents tree sapling establishment, are mutually exclusive and self‐reinforcing drivers of biome distribution in savanna–forest mosaics. We investigated how shade depth, represented by canopy leaf area index ( LAI ), is generated by adult trees across savanna–forest boundaries and how a shade gradient filters tree functioning, and grass composition and biomass. Forest trees exerted greater shading through increased stem density and greater light interception per unit biomass. A critical transition at LAI c . 1.5 was linked to tree shifts from savanna to forest species, functional shifts from fire‐tolerant to light‐competitive species, and grass composition shifts from C 4 to C 3 pathways. A second transition to grass fuel loads too low to support fires, occurred at a lower canopy density ( LAI > 0.5), accompanied by shifts in C 4 subtype dominance. This pattern suggests that shade suppression of grass biomass is an essential first step for the maintenance of alternative stable states.